A bit of brain tissue near the top of the head may be the body’s fact-checker. Called the supplementary motor cortex, this brain region monitors the body’s action and sends an alert when a mistake is made, scientists report in the Feb. 21 Science.

By eavesdropping on neurons in the brains of five people who were being treated for epilepsy, French researchers found that neurons in the supplementary motor cortex were active when people made a mistake. In this case, th...